Flat substrates, such as semiconductor substrates, are stressed during certain processing steps, e.g., depositing or etching thin films. Stress in deposited layers can warp the substrate, which can adversely affect subsequent process steps, device performance, reliability and line-width control. Thus, it is desirable to measure the radius of curvature of a substrate as well as measure the stress on a substrate that is associated with a processing step.
There are many measurement tools available for measurement of the radius of curvature and analysis of the stress associated with certain processing steps on substrates. Most of the available tools for the semiconductor industry use a laser displacement sensor to measure the radius of curvature and to monitor the change in radius of curvature of the substrate before and after the processing step. Generally, radius of curvature is used to describe the bow of the substrate over a larger scale, e.g., the diameter of the substrate. Typical metrology devices, however, do not measure the local topography, and thus, provide only a global Bow/Stress measurement.